Early methods for olefin metathesis or olefin disproportionation were performed using ill-defined metathesis catalyst based on group VI and VII transition metals (W, Mo, and Re). The advent of well-defined Grubb's ruthenium type catalysts introduced stability under ambient conditions and functional group tolerance to metathesis chemistry. Olefin metathesis using Grubb's type ruthenium catalysts are traditionally performed at temperatures ranging from 20 to 60° C. Degradation or olefin migration can be problematic at elevated temperatures. Access to elevated reaction temperatures can potentially enhance metathesis chemistry by unlocking products previously unrealized due to thermodynamic constraints. Metathesis polymerization above the polymer's melting temperature can benefit by allowing the resultant polymer chains to remain unconstrained by crystallization to increase chain diffusion and molecular weight during polymerization.
In the case of metathesis polymerization, acyclic diene metathesis polymerization (ADMET) has been shown to be a useful technique for synthesizing precision functional polyolefin derivatives. The resultant polymers are highly crystalline, exhibiting high melting temperatures. As a result, the polymers are synthesized in solution or solid state. Both techniques limit efficient step growth polymerization, restricting the molecular weight attainable. Additionally, solution polymerization requires the application of vacuum during polymerization. Negative pressure is necessary to remove gaseous ethylene and drive the metathesis equilibrium towards polymerization. Weychardt et al. Organometallics, 2008, 27 (7), pp 1479-85 developed a procedure using high boiling point solvents thus light vacuum could be applied. While this method is valuable, solvent purification is required and the use of solvent is cumbersome for scale up and industrial process.
Gaines et al. Macromol. Chem. Phys. 2016, 217, 2351-9 demonstrated precision aliphatic polysulfones synthesized via ADMET. The polymers displayed high melting temperature which increased with increasing sulfone content. Both bulk and solution polymerization techniques were ineffective at producing high molecular weight polymer. The high melting temperature of the polymer limited polymer molecular weight using bulk synthesis with Grubb's 1st generation catalyst. Raising the polymerization temperature to above the melting temperature (Tm) of unsaturated polymer product (about 130° C.) degrades the catalyst. Solution polymerization was performed; however, polymer insolubility limited the polymer's molecular weight. The polysulfones are a prime candidate for bulk high-temperature metathesis polymerization.
Hence there remains a need for carrying out metathesis reactions at temperatures in excess of 100° C.